The present invention relates to an improved current source arrangement having a plurality of current sources. A current source can be optimized for a high capacitance. A different current source can be optimized for a high power output.
The present invention relates, in particular, to an improved current source arrangement for an electrically driven vehicle.
For the purpose of power scaling in electrochemical energy stores in a vehicle, capacitance-optimized rechargeable battery cells and power-optimized rechargeable battery cells or double-layer capacitors are installed in mixed fashion in a rechargeable battery arrangement, which is also referred to in the prior art as a dual store. Generally, a string or a plurality of strings of capacitance-optimized cells are connected in parallel with a string or a plurality of strings having power-optimized cells. The strings are generally coupled by means of a DC/DC converter, which is connected in parallel with the strings. The DC/DC converter balances different voltages between the strings.
DE 20 2009 017 862 U1 and DE 20 2008 017 499 U1 describe parallel circuits of batteries.
DE 10 2013 209 069 A1 discloses a battery assembly having high-energy cells and high-power cells.
A disadvantage of the prior art is that the DC/DC converter has to be designed for the maximum peak power of the coupled string of rechargeable battery cells. A DC/DC converter of this kind is complex, requires a relatively large amount of installation space, gives rise to high costs and causes a high power loss.
DE 10 2015 202 975.1, the entire disclosure of which is hereby incorporated by reference herein, describes a rechargeable battery arrangement having a DC/DC converter having first rechargeable battery cells connected in parallel, wherein the DC/DC converter is connected in series with second rechargeable battery cells.
The invention addresses the object of providing an improved current source arrangement that has a plurality of current sources.
The object of the invention is achieved by a current source arrangement, by an electric drive and by a method for supplying power, in accordance with embodiments of the invention.
A current source arrangement according to the invention comprises a first current source having a first terminal and a second terminal, a second current source having a first terminal and a second terminal, and a DC/DC converter. The DC/DC converter has a first terminal pair and a second terminal pair. The DC/DC converter is configured to convert a first DC voltage applied to the first terminal pair to a DC voltage output at the second terminal pair. The DC/DC converter can be configured to convert a first DC voltage applied to the second terminal pair to a DC voltage output at the first terminal pair. The first terminal pair of the DC/DC converter is connected in parallel with the first current source, and the second terminal pair of the DC/DC converter is connected in series with the second current source. The second terminal pair of the DC/DC converter and the second current source are connected in parallel with the first current source.
In the current source arrangement according to the invention, the DC/DC converter does not have to convert all of the power that is output by a current source. Said DC/DC converter can therefore be designed in a substantially simpler manner, as a result of which installation space, weight, outlay and power loss are reduced. The performance of the current source arrangement according to the invention is also increased. The first current source can be set up to have a higher output voltage than the second current source. In the current source arrangement according to the invention, the DC/DC converter can be operated in such a way that the two current sources output current to a load in parallel. This operating situation is desirable when it is intended for an electric drive to generate a high torque. The current source arrangement according to the invention can be operated in another operating situation in such a way that the voltage of the first current source and the voltage of the second current source are connected in series by way of the DC/DC converter. This mode of operation may be desirable, for example, when an electric drive is operated at a high rotational speed.
A first terminal of the first terminal pair and a first terminal of the second terminal pair of the DC/DC converter can have the same potential. As a result, the voltages at the first terminal pair of the DC/DC converter, at the second terminal pair of the DC/DC converter and at the first terminal of the first current source are set to the same reference potential.
The first terminal of the first current source can be coupled to the first terminal of the first terminal pair of the DC/DC converter and to the first terminal of the second terminal pair of the DC/DC converter. The second terminal of the first current source can be coupled to the second terminal of the second current source and to the second terminal of the first terminal pair of the DC/DC converter.
The current source arrangement can have a first terminal and a second terminal. A load, for example an inverter that supplies power to an electric machine, can be connected to the first terminal and the second terminal of the current source arrangement. The first terminal of the first current source can be coupled to the first terminal of the current source arrangement. The second terminal of the first current source can be coupled to the second terminal of the current source arrangement by way of a first switch. The second terminal of the second current source can be coupled to the second terminal of the current source arrangement by way of a second switch. The first and the second switch may be a so-called contactor.
Depending on the desired operating state, the first and the second switch can be connected in such a way that the current in the arrangement flows from the two current sources and the DC/DC converter in the desired manner. When the current source arrangement is charged, the first switch and the second switch can also be connected in such a way that the current sources are charged properly.
The current source arrangement according to the invention can have a first charging terminal, which is coupled to the first terminal of the second terminal pair of the DC/DC converter, and a second charging terminal, which is coupled to the second terminal of the second current source. As a result, the charging current for the first current source can be set by means of the DC/DC converter.
The first current source and/or the second current source can have a rechargeable battery optimized for a high capacitance, a rechargeable battery optimized for a high current output, a capacitor, a supercapacitor, a series circuit of rechargeable battery cells, a series circuit of rechargeable battery cells optimized for a high capacitance, a series circuit of rechargeable battery cells optimized for a high current output and/or a fuel cell. In one embodiment, the first current source can be a series circuit of rechargeable battery cells optimized for a high capacitance and/or a rechargeable battery optimized for a high capacitance. The second current source can be a series circuit of rechargeable battery cells optimized for a high current output and/or a rechargeable battery optimized for a high current output.
The current source arrangement can have a control device. The control device can be configured to actuate the DC/DC converter, the first switch and the second switch in such a way that the first switch and the second switch are closed. The control device can actuate the DC/DC converter in such a way that a current flows through the first current source and through a load connected to the terminals of the current source arrangement. The DC/DC converter is furthermore actuated in such a way that a current flows through the first current source and through the first terminal pair of the DC/DC converter. In this first operating situation, the DC/DC converter is actuated in such a way that a current flows through the second current source and through the second terminal pair of the DC/DC converter and through the load connected to the terminal pair of the current source arrangement. The current of the first current source furthermore flows to the load connected to the terminal pair of the current source arrangement. In this first operating situation, the DC/DC converter can be operated by means of current regulation, wherein the current at the second terminal pair of the DC/DC converter regulates the load distribution between the two current sources.
The difference between the voltage of the first current source and the second current source can be applied across the second terminal pair of the DC/DC converter. In this operating situation, the voltage of the first current source can be applied at the load, said voltage being identical to the sum of the voltage of the second current source and the voltage across the second terminal pair of the DC/DC converter. This operating situation can be used, for example, for accelerating an electrically driven vehicle, since, in this operating situation, the electric machine has to generate a high torque, for which reason the inverter requires a high link circuit current.
In a second operating situation, the control device can actuate the first switch and the second switch in such a way that the first switch is open and the second switch is closed. In this operating situation, the DC/DC converter is actuated in such a way that a current flows through the first current source and through the first terminal pair of the DC/DC converter. The DC/DC converter is furthermore actuated in such a way that a current flows through the second current source and through the second terminal pair of the DC/DC converter and through the load connected to the terminals of the current source arrangement.
The voltage at the second terminal pair of the DC/DC converter can be regulated. As a result, a voltage that is higher than the voltage of the first current source can be generated at the terminals of the current source arrangement.
In this embodiment, the sum of the voltage of the second current source and the voltage across the second terminal pair of the DC/DC converter is applied to the terminals of the current source arrangement. The current source arrangement according to the invention can therefore generate a high link circuit voltage, as a result of which the efficiency of the inverter can be increased depending on the operating point of the electric drive. This operating situation may be suitable when the electric machine is operated at a high rotational speed.
In a third operating situation, the control device actuates the first switch and the second switch in such a way that the first switch is open and the second switch is open. The control device actuates the DC/DC converter in such a way that a current flows through the charging terminals and through the second current source and through the second terminal pair of the DC/DC converter. A current therefore flows through the first terminal pair of the DC/DC converter and through the first current source. In this operating situation, the first current source and the second current source can be charged. In this operating situation, the current across the first terminal pair of the DC/DC converter is controlled or regulated. A voltage at the charging terminal of the arrangement that is higher than the voltage of the second current source is furthermore increased as a result. Since the charging power depends linearly on the charging voltage and since the charging current in a charging station is generally limited, the charging power of the current source arrangement increases.
The invention also relates to an electric drive having an electric machine, which is connected to first terminals of an inverter. The electric drive also comprises the current source arrangement described above, which is connected to two terminals of the inverter. The inverter generates from the DC voltage of the current source arrangement an AC signal, for example a three-phase AC signal, which is applied to the electric machine.
The invention also relates to an electrically driven vehicle having the electric drive described above. The electrically driven vehicle can have a hybrid drive, a plug-in hybrid drive or a fully electric drive.
The invention also relates to a method for supplying power to an electrical load. In a first operating situation, the method has the steps of causing a current to flow through a first current source and through the load, the step of causing a current to flow through the first current source and through a first terminal pair of a DC/DC converter and the step of causing a current to flow through a second current source and through a second terminal pair of the DC/DC converter and through the load. This operating situation corresponds to the first operating situation, which has been described above in terminal with the current source arrangement according to the invention. For the sake of conciseness, said operating situation is not described again.
In a second operating situation, the method comprises the step of causing a current to flow through the first current source and through the first terminal pair of the DC/DC converter and the step of causing a current to flow through the second current source and through the second terminal pair of the DC/DC converter and through the load. This operating situation corresponds to the second operating situation described in terminal with the current source arrangement according to the invention. For the sake of conciseness, said operating situation is not described again either.
In a third operating situation, the method can have the step of causing a current to flow from a charging current source through charging terminals and through the second current source and the second terminal pair of the DC/DC converter and the step of causing a current to flow through the first terminal pair of the DC/DC converter and through the first current source. This operating situation serves to charge the first current source and the second current source.
The method can thus be developed further, as has been described above with respect to the current source arrangement.
The invention also relates to a computer program product, which executes the steps described above when it is loaded into a memory of a computer having a processor.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.